The invention relates to a multi-layered article, more particularly to a multi-layered article having a thermoset polyurethane layer bonded to a second polymeric layer and a method for making a multi-layered article.
Thermoset poyurethane layers are desirable for use as protective layers on substrates. Conventional polyurethanes function well when they are utilized as laminates or coatings that are not subjected to subsequent process steps that require deformation of stretching of a cured thermoset polyurethane.
Thermoset polyurethanes are durable and can provide desirable aesthetic value to certain substrates. However, it often desirable to utilize polyurethane coatings on three dimensional articles. Conventional thermoset polyurethanes are generally rigid and have limited elongation properties. The limited elongation creates problems when attempting to thermoform polyurethanes in conventional molding applications. Additionally, the thermoforming of polyurethanes requires the use of elevated temperatures to enable the elongation of the polyurethane. The elevated temperatures can create both mechanical and aesthetic problems with the polyurethane. Additionally, elevated temperatures can adversely affect the gloss of the exposed surface of the polyurethane because of the direct contact of the exposed surface with the mold surface.
Other potential problems with conventional thermoset polyurethanes are created by the coating environment during the formation of the polyurethane coating. The process of forming the polyurethane coating on the substrate often takes place in an open environment. This can create surface defects such as bubbles, dust, dirt, etc. in the exposed surface of the polyurethane.
There is a need in the art for a thermoset polyurethane that is capable of greater elongation to enable improved thermoforming processes. Additionally, there is a need for a thermoset polyurethane that is capable of extensive thermoforming without adversely affecting the aesthetic properties of the finished polyurethane.
The present invention provides a multi-layered article that can function as a coating when applied onto various elements or substrates. The multi-layered article possesses physical characteristics that enable the use of the inventive article as either a protective or aesthetic coating on laminates or thermoformed articles.
The multi-layer article comprises a first layer of a thermoset polyurethane. A second layer of a polymeric composition is bonded to the first layer. The polyurethane has available isocyanate groups prior to the application of the second layer. The second layer is applied onto the first layer in a pre-polymeric or polymeric state wherein the material has carboxyl groups and a cross-linking agent.
The polyurethane is generally a two part thermosettable polyurethane having a hydroxyl component and an isocyanate component. The thermosettable polyurethane has available isocyanate prior to the application of the pre-polymeric or polymeric second layer. The term available isocyanate groups means that the thermosettable polyurethane possesses at least some amount of isocyanate that has not reacted with the hydroxyl component in the polyurethane. Therefore, the available isocyanate has the ability to react with components in the second pre-polymeric or polymeric layer. Available isocyanate groups in the polyurethane can be obtained in various manners. For example, partial curing of the thermoset polyurethane or the use of excess isocyanate in the polyurethane can result in available isocyanate.
The second layer is a pre-polymeric or polymeric material having carboxyl groups and a cross-linking agent. The cross-linking agent can react with the available isocyanate (NCO) groups of the polyurethane and also react with the carboxyl groups in the second layer. The reaction of the cross-linking agent with components in each layer can enhance the bond between the layers.
In an alternative embodiment, the present inventive article includes available hydroxyl or amine groups in the polymeric and pre-polymeric layer. The available hydroxyl groups or amine groups either replace or supplement the carboxyl groups and cross-linking agent. The available hydroxyl groups or amine groups are capable of reacting with the isocyanate groups of the first layer of a thermosettable polyurethane.
The resulting multi-layered article exhibits an improved elongation over conventional thermoset polyurethanes. The article of the present invention has an elongation test result of at least 15% at 25xc2x0 C. The improved elongation permits thermoforming of the article at temperatures of 100xc2x0 C. or less.
In a preferred embodiment, the thermoset polyurethane is produced utilizing a primary isocyanate. The resulting multi-layered article has a urethane linkage as indicated by FTIR test results at 25xc2x0 C., taken from either the first or second layer surface. The urethane linkage exhibits the unique property of having a hydrogen bonded carbonyl peak equal to or smaller than a free carbonyl peak.
The invention also provides for a method of producing a multi-layer article by coating a thermosettable polyurethane composition, optionally, partially curing to form a layer of polyurethane having free isocyanate (NCO) groups, and coating a polymeric composition having carboxylic groups and a cross-linking agent on top of the first layer.
For purposes of the present invention, the following terms used in this application are defined as follows:
xe2x80x9chydroxyl componentxe2x80x9d means one or more diols, one or more polyols, or mixtures thereof;
xe2x80x9cisocyanate componentxe2x80x9d means one or more diisocyanates, one or more polyisocyanates, or mixtures thereof;
xe2x80x9cpolyolxe2x80x9d means a compound having a hydroxyl (OH) functionality of three or more;
xe2x80x9cdiolxe2x80x9d means a compound having a hydroxyl functionality of two;
xe2x80x9cdiisocyanatexe2x80x9d means a compound having an isocyanate (NCO) functionality of two;
xe2x80x9cPolyisocyanatexe2x80x9d means a compound having an isocyanate (NCO) functionality of three or more;
xe2x80x9cprimary isocyanatexe2x80x9d means a carbon atom upon which the isocyanate group is attached to also has two hydrogen atoms;
xe2x80x9ccatalystxe2x80x9d means a material that can change the speed of a chemical reaction;
xe2x80x9cpolymerizexe2x80x9d or xe2x80x9ccurexe2x80x9d means to alter the physical state and or chemical state of the composition, to make it transform from a fluid to less fluid state, to go from a tacky to a non-tacky state, to go from a soluble to insoluble state, to decrease the amount of polymerizable material by its consumption in a chemical reaction, or go from a material with a specific molecular weight to a higher molecular weight;
xe2x80x9cpartially curedxe2x80x9d polyurethane means a polyurethane having available isocyanate groups within the polyurethane that are capable of further reaction with active hydrogen containing materials, for example, hydroxyl groups, amine groups, etc.;
xe2x80x9cthermosettable polyurethanexe2x80x9d means a polyurethane having available isocyanate groups for further reaction with hydroxyl groups; and
xe2x80x9cpolymericxe2x80x9d means a composition having less than 5% by weight monomers excluding the cross-linking agent;
xe2x80x9cpre-polymericxe2x80x9d means a monomeric or oligomeric composition or mixtures thereof, or a blend of polymeric and monomeric or oligomeric compositions;
xe2x80x9cequivalent weightxe2x80x9d of the hydroxyl components corresponds to the molecular weight of the material divided by the number of hydroxyl functionalities.
Other features and advantages will be apparent from the following description of the preferred embodiments thereof, and from the claims.